Ink-jet recording is performed to record images and letters by ejection of minute ink droplets employing various working principles onto a recording sheet, such as paper, exhibiting advantages of relatively high speed, low noise and simple multi-color printing.
Recently, ink-jet printers have been developed of enhancement in image quality which approaches that of conventional silver halide photography, and thus, it is desired that a recording sheet also duplicates conventional photographic quality, and in addition reproduces the aesthetic property of silver halide photography (such as glossiness, smoothness and stiffness).
As one of the methods to reproduce said aesthetic properties of silver halide photography, a so-called swelling type recording sheet has become common, comprised of a hydrophilic binder such as gelatin and polyvinyl alcohol, applied onto a substrate. However, this method has drawbacks of low ink absorption rate, tendency of a sticky surface after printing, and image bleeding due to ambient humidity during storage. Specifically, ink droplets blend easily before they are absorbed due to low ink absorption rates, resulting in bleeding among different colors and beading or unevenness in the same color. Thus, achievement of the desired silver halide photographic image quality has not yet been realized to meet expectation.
So-called porous type recording sheets are becoming the main types instead of previous swelling types. A high ink absorption rate is a major feature due to effective ink absorption into minute voids.
Specifically, high glossiness and superior ink absorbability can be achieved by the combination of water soluble dye ink and a porous type ink jet recording medium, resulting in approaching the photographic image level, with regard to image quality.
On the other hand, storage stability of ink jet images is often compared with that of silver halide photography as image quality of ink jet images is improved. Specifically, regarding water soluble dye ink, pointed out is deterioration of ink jet images such as that accompanying transmission of coloring materials causing poor water fastness and bleeding of images, and chemical reaction of coloring materials causing inferior light stability and low oxidizing gas resistance.
As mentioned above, a number of studies have been made to achieve image quality comparable to silver halide photographic levels. As examples of light stability improvement, many techniques are disclosed, such as JP-A Nos. 57-74192, 57-87989, 57-74193, 58-152072, 64-36479, 1-95091, 1-115677, 3-13376, 4-7189, 7-195824, 8-25796, 11-321090, 11-277893, and 2000-37951 (the term JP-A means Japanese Patent Application Publication).
Regarding porous type recording sheets, they tend to cause problems such as discoloration in the presence of specific gases, specifically color-fading by so-called oxidizing gases, due to their porous structure in addition to other light stability drawbacks. Specifically, phthalocyanine series water-based dyes employed in common color ink jet printers tend to result in such discoloration.
The mechanism of this discoloration property is not yet fully clarified, but it is assumed that the minute porous structure has an excessively large surface area and the inorganic particles used therein have reactive surfaces, resulting in decomposition of dyes by minute quantities of reactive gases such as ozone, oxidants, SOx and NOx in the ambient air.
Techniques to minimize such discoloration problems are disclosed, for example, in JP-A Nos. 63-252780, 64-11877, 1-108083, 1-216881, 1-218882, 1-258980, 2-188287, 7-237348, 7-266689, and 8-164664. These discoloration problems are more prominent deteriorating problems in recording sheets exhibiting photograph image quality having an enhanced minute porous structure, and thus, the relevant art for improvement has not been sufficient to obtain the desired effects, calling for further fundamental improvement.
One of the measures to counter the foregoing problems is to use a swelling type recording sheet, but on the other hand, it is very difficult to improve the critical matter of slow ink absorption rate by the use of this type of recording sheets. Alternatively, for example, a gas insulating method which uses a laminating process for prints and framed printed photos, and a gas insulating layer developing method have been very effective, but in both cases after-treatment is necessary and this extra process is an additional production burden troublesome. The gas insulating layer developing method provides a gas insulating layer using a heat or pressure treatment after printing on the recording sheet, which contains thermoplastic particles in the surface layer, and is disclosed in JP-A Nos. 53-27426, 59-222381, 62-271781, 11-157207, 11-245507, and 2000-71608.